1. Field of the Invention
The present invention relates to a thermal cutter for the cutting of a moving textile material web, especially a web of textile artificial fiber or plastic material such as polyethylene or polypropylene. Such cutting is usually done as the web comes off a loom and before the web is wound. The cutting may be done to remove selvedge by cutting off outer edges of the cloth, and may also be done in central areas of the web to make narrow webs such as tapes.
2. Prior Art
The cutting of a moving web of plastic textile material is commonly done by thermal cutters such as hot wires. These have the property that in melting the material they also seal the edges and lessen the tendency of the edges of the material to unravel; unravelled edges can cause problems in winding and subsequent processing. One known thermal cutter device is that sold by Loepf Bros. Ltd (Gebruder Loepf AG) of Switzerland, under the designation xe2x80x9cThermocut TC-1Sxe2x80x9d. In this the material is cut by an electrically heated wire having a U-shaped portion which cuts through the material as it passes in a direction generally parallel to the plane of the U-shaped portion, but which plane may be slightly off-set at an acute angle to the web direction plane. The hot wire both cuts and seals the material, with the sealing being dependent on the type of material and the angle at which the cutter is set. It is recommended by this company that the wire U-shaped portion be set parallel to the web travel direction for heavy fusing and thick edges, and at a small angle (of say 5 or 10xc2x0) to this direction for light fusing and thin edges. In my experience with the Loepf apparatus, there is a tendency among workers to ignore the recommendations concerning angles, leading to unsatisfactory sealing of the edges. Also, where a rather loose weave material is used, the sealing is often inadequate to prevent the strands of material being pulled apart by tension applied to the web.
Further examples of prior art showing this type of hot wire cutting apparatus for moving textile webs are shown in the following U.S. patents:
U.S. Pat. No. 4,572,245, issued Feb. 25, 1986 to Gachsay;
U.S. Pat. No. 5,101,094, issued Mar. 31, 1992 to Keller et al.;
U.S. Pat. No. 5,452,633, issued Sep. 26, 1995 to Speich; and
U.S. Pat. No. 5,806,393, issued Sep. 15, 1998 to Saporiti.
The Keller et al. patent is assigned to Loepf A. G., and shows various modifications of the Thermocut TC-1S design. These modification include using a wire which is relatively thin and sharp so that it can cut at temperatures not substantially higher than the melting temperature, and using a wire which is S-shaped when viewed perpendicularly to the plane of the material being cut. The devices shown in this patent still require that, for satisfactory operation, the wire be set at particular angles, so this does not meet the problem posed by operators who do not adjust the angle properly.
The Gachsay patent is concerned with a shield for preventing cooling of the wire. The Speich and Saporiti patents are concerned with special arrangements of heated wire.
All the prior art referred to above relies on the heated wire, or a part of the wire, to perform the sealing operation as the textile passes over the wire.
The present invention provides an arrangement in which reliance for sealing the cut edges of the textile is not placed on the hot wire itself or the positioning of the wire; instead a further sealing member is provided just downstream of the wire or cutting element.
In accordance with a first aspect of the invention, a device for cutting a moving web of textile material as it passes the device, and for sealing the cut edges of the material, comprises:
an electrically heated cutting member capable of severing the material as it passes the cutting member, and
an electrically heated sealing member downstream from the cutting member relative to the direction of the moving web and positioned to contact and seal the edges of material cut by the cutting member as the edges passes over the sealing member, the sealing member having means for maintaining the sealing member at a suitable temperature for sealing the edges, the sealing member having a width larger than that of the cutting member transverse to the direction of the moving web. The sealing member temperature will normally be different from, and may be substantially higher than, the cutting member temperature.
The sealing member may have a convexly curved surface adjacent to but spaced from the cutting member and which contacts the cut edges as they leave the cutting member.
In accordance with another aspect of the invention, the device has:
first and second electrical terminals, and
an electrically conductive wire connected between the terminals, the wire having first and second portions;
wherein a first wire portion provides a textile cutting wire which extends transversely relative to the direction of movement of the moving web;
and wherein a second wire portion provides a heating element for a sealing member having a convexly curved surface and incorporating the second wire portion; the sealing member also being disposed transversely to the web direction and immediately downstream of the cutting wire relative to the web movement.
The convexly curved surface of the sealing member is several times greater than the diameter of the cutting wire and is such that, with a current passing through the wire, the sealing member is heated to a temperature suitable for sealing the cut edges, which temperature is usually higher than that of the cutting wire and serves to seal the edges of the material cut by the wire.
Preferably, the first and second wire portions are substantially parallel and are joined by a short wire section extending between ends of the cutting wire and an adjacent end of the sealing member remote from the electrical terminals.
The sealing member preferably has a width transverse to the direction of web movement which is at least 5 times greater than the cutting member width.
The sealing member may comprise electrically insulating, thermally conductive material surrounding the second wire portion, and a metal sheath surrounding the electrically insulating material.
The invention also includes a process for the thermal cutting of a moving web of textile material, wherein the moving material is contacted firstly by a heated cutting member capable of severing the material, and immediately afterwards edges which have been cut by the cutting member are contacted by a sealing member which is separate from the cutting member and which is maintained at a temperature which is suitable for sealing the cut edges; this sealing temperature will be above the melting point of the material and may be substantially higher than that of the cutting member.